I had a XTM front 1/8 spring set laying around, and used the blue set:
http://www.hobbypeople.net/gallery/149354.asp
Without any preload the rear sits higher than I would like. The springs might just need to be cut down, but I haven't gotten enough driving time in to determine whether or not they are too stiff.
SH Z-Car, Custom Crawler, 8s Savage,
12s XTM XLB 1/7 buggy,
4wd 4-link rear/IFS Pro4 truck,
Custom Hyper 10 Short Course,
Belt-Drive Mammoth ST 1/8 truggy, 4s 17.5 MM Pro HPI Blitz